Additive compositions and methods for papermaking with high-kappa furnishes

ABSTRACT

A strength additive composition for papermaking processes using high-kappa furnish is disclosed. The composition comprises an aqueous media and a glyoxalated polyacrylamide (gPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150 nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda. A method of preparing the composition is also disclosed, and may be carried out in situ during a papermaking process (i.e., as an on-site method). A process of forming paper with the composition is also disclosed, and comprises combining the composition with an aqueous suspension of cellulosic fibers, forming the cellulosic fibers into a sheet, and drying the sheet to produce a paper.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and all benefits of U.S. Provisional Application No. 63/369,985, filed Aug. 1, 2022, the content of which is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to additive compounds and compositions for papermaking and, more specifically, to low-charge high-molecular weight glyoxalated polyacrylamide (gPAM) resins optimized for high-kappa furnishes, and methods of making and using the same.

BACKGROUND

Papermaking is a complex process in which paper is prepared from pulp (e.g. wood), water, filler, and various chemicals. Paper manufacturing is among the most water intensive industries, as the processes include numerous stages reliant on substantial amounts of water and aqueous solutions being added to the cellulosic fibers (i.e., the “inflow stream”) to give a furnish, and eventually separated from the furnish (i.e., the “effluent stream”) to give the final product. In the course of a typical papermaking process, a relatively concentrated aqueous slurry of cellulosic material (i.e., “thick stock”) is diluted by addition of water to give a relatively diluted slurry of cellulosic material (i.e., “thin stock”), which is used to prepare a paper web that must be dewatered to give the final product. The type of cellulosic material varies depending on the pulp and pulping process(es) used to prepare the furnish. For example, mechanical, chemical, and/or semi-chemical pulping processes may be used to break down and/or separate cellulosic materials into separate components, including cellulosic fibers, which may be further by various chemical and/or mechanical processes (e.g. bleaching, screening, etc.) to prepare a given pulp.

The starting material fed into the pulping process may also be varied and, depending on the pulping process, will impact the composition and utility of the furnish prepared. For example, both virgin and recycled pulps are commonplace throughout the papermaking industry. Recycled pulps are used for products such as tissue, as the prior processing allows for higher cellulose contents and reduced impurity contents compared to virgin pulp prepared under similar process conditions. However, recycling processes are relatively more expensive than virgin pulp production, and the pulping and recycling processes weaken and shorten fibers, thus limiting the paper cycle time upon each subsequent use. Comparatively, virgin pulps are more sustainable and prepare products with longer paper cycle times. However, virgin pulps require refining steps to remove impurities, and may have limited uses due to residual impurities (e.g. lignin, anionic trash, etc.) remaining with the fibers after the pulping process. In some cases, such as with unbleached kraft (UBK) processes, the pulp includes higher levels of dissolved and colloidal anionic materials, leading to “difficult” furnishes that resist conventional methods of achieving targets for retention, draining, formation, and/or strength.

Throughout the papermaking process, various chemical additives are employed to improve particular properties of the process (i.e., “process aids”) and/or the final product being prepared (i.e., “functional aids”). Examples of processes aids include defoamers and antifoams, retention aids, biocides, drainage aids, formation aids, etc. Examples of functional additives include strength aids, e.g. for imparting temporary wet-strength (TWS), wet-strength (WS), and/or dry-strength (DS) to the final product.

In view of the number and complexity of required stages in a given papermaking process, and the number and amounts of additives utilized in each stage, there is increasing demand for additives that provide both process and functional improvements to a given processes. Unfortunately, however, achieving some sought after improvements may lead to a decrease in other performance factors. For example, achieving high retention, which can lead to improvements in the strength of the final product, can lead to reduced drainage and formation. Using conventional high molecular weight drainage aids can dive excellent drainage and retention, but offer little to no strength benefits, and in some instances even result in a reduced strength due to over-flocculation. Certain DS aids like polyamidoepichlorohydrins (PAE) can give excellent dry strength, but offer little to no drainage benefits and have limited repulpability. Complicating matters further, the efficiency of any given solution is strongly furnish dependent, with some of the best known dry strength and/or drainage aids failing under desired conditions, e.g. due to fines content, lignin content, and/or conductivity of the furnish system. For example, conventional dry and wet strength agents typically require higher loadings, yet exhibit reduced performance, in the difficult furnishes described above, and often limit the repulpability of the resulting fiber. As such, while there are programs to address these furnish derived performance reductions, there is a still present need for additives that provide exceptional dewatering and good dry strength in even the most challenging furnish systems (e.g. UBK, etc.).

One category of chemicals being increasingly explored for multi-use additive application includes glyoxalated polyacrylamide (gPAM) resins, which have been utilized in the paper industry for many years as processes aids, e.g. for improving water drainage during the papermaking process, and also as functional additives, e.g. for imparting temporary wet-strength (TWS), wet-strength (WS), and dry-strength (DS) to the final paper(s) being prepared. Typical gPAM resins are prepared by glyoxalating polyacrylamides (PAM), i.e., by reacting glyoxal with a PAM or PAM copolymer, such as those prepared from acrylamide (AM) and various anionic or cationic monomers. As but one example, diallyldimethylammonium chloride (DADMAC) is a cationic monomer utilized to prepare poly(AM/DADMAC) copolymers, which may be used as a prepolymer in a glyoxalation reaction to give the corresponding gPAM resins (i.e., glyoxalated poly(AM/DADMAC)). Unfortunately, conventional gPAM resins suffer from numerous drawbacks associated with production, storage, and use. For example, while many commercial gPAM resins are known to perform as exceptional strength aids, such resins typically underperform in difficult furnishes, especially with respect to dewatering and drainage. These conventional gPAM resins also exhibit reduced performance in high lignin environments, and thus have limited utility in difficult furnishes.

BRIEF SUMMARY

An additive composition for papermaking is provided. The additive composition comprises an aqueous media and a glyoxalated polyacrylamide (gPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150 nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda. The additive composition may be prepared in situ during a papermaking process (i.e., as an on-site gPAM resin).

A method of preparing the additive composition (the “preparation method”) is also provided. The preparation method comprises preparing a cationic acrylamide (cAM) prepolymer having a cationic monomer content of less than about 3.5 mol %, and selectively glyoxalating the cAM prepolymer in the aqueous media to give the gPAM resin, thereby preparing the additive composition. The cAM prepolymer comprises a cationic monomer content of from about 1 to about 3 mol %, and may exhibit a reduced solution viscosity (RSV) of from about 0.5 to about 1.8 dL/g. Selectively glyoxalating the cAM prepolymer comprises controlling the concentration of the cAM prepolymer in the aqueous media during glyoxalation. The preparation method may be carried out in situ during a papermaking process (i.e., as an on-site method).

A process of forming paper with the additive composition (the “process”) is also provided. The process comprises: (1) providing an aqueous suspension of cellulosic fibers; (2) combining the additive composition with the aqueous suspension or preparing the additive composition in the presence of the aqueous suspension; (3) forming the cellulosic fibers into a sheet; and (4) drying the sheet to produce a paper. The process may be carried out using an aqueous suspension having a kappa number of at least about 30, and without the use of polyamidoepichlorohydrins (PAE).

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the instant composition or method. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. Conventional techniques related to the compositions, methods, processes, and portions thereof set forth in the embodiments herein may not be described in detail for the sake of brevity. Various tasks and process steps described herein may be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein for being well-known and readily appreciated by those of skill in the art. As such, in the interest of brevity, such conventional steps may only be mentioned briefly or will be omitted entirely without providing well-known process details.

An additive composition comprising a high-performance strength agent is provided, along with a method of preparing and a process for using the same. The strength agent provides both wet and dry strength improvements, and is optimized for tolerating high-lignin environments, thus enabling economical production of products from difficult furnishes. The additive composition may thus be used to add strength to linerboard and other products from virgin furnishes, allowing the use of underweighting, reduced refining, use of higher kappa furnish, and other cost-saving measures, while improving overall fiber yield.

The additive composition comprises a glyoxalated polyacrylamide (gPAM) resin as the dry strength agent. The gPAM resin has very low charge and a high-molecular weight, each of which may be selectively tailored via the method provided herein. The gPAM resin exhibits excellent performance in difficult furnishes and provides good strength—both wet and dry—to products. Moreover, the gPAM resin is repulpable, and thus may provide benefits of repulpable wet-strength. As such, the additive composition may be utilized in papermaking processes to provide improvements and advantageous thereto. In specific application using difficult furnishes, the additive composition demonstrates improved performance over conventional strength additives, enabling production of improved products such as packaging made from unbleached kraft (UNK) virgin furnishes.

As described and demonstrated in the embodiments and examples herein, it has been surprisingly discovered that the gPAM resin of the additive composition can be prepared with a high weight average molecular weight (Mw), a low overall charge, and a high density via the method described below. Compared to conventional techniques, the method of the present embodiments decouples the Mw and/or charge of the product gPAM resin from the Mw and/or charge of the prepolymer utilized in to prepare the gPAM resin. As such, the additive composition can provide improved functionality and performance by providing the gPAM resin with selectively prepared Mw and charge, without the drawbacks or deficiencies associated with conventional techniques relying on prepolymer properties for performance.

The additive composition comprises the gPAM resin and the aqueous media. The aqueous media is not particularly limited, and may comprise, alternatively may be, any aqueous composition compatible with the gPAM resin and/or the components used to prepare the same. In this fashion, the aqueous media may be a water-based solution or suspension, optionally including additional components, such as process water from a papermaking operation, or simply an aqueous carrier vehicle used in the preparation of the gPAM resin.

Typically, the additive composition comprises the gPAM resin in the aqueous media in functional amount, i.e., in a solids content that maximizes the amount of gPAM resin while maintaining a useful flowable state of the composition. In this sense, the gPAM resin may be present in an amount of from greater than 0 wt. % to less than the gel point of the gPAM resin in the aqueous media. In some embodiments, the gPAM resin is present in an amount of from about 1.2 to about 6%, such as from about 1.2 to about 5, alternatively from about 1.3 to about 4, alternatively from about 1.4 to about 3, alternatively from about 1.95 to about 2.45% based on the aqueous media (i.e., as % solids). However, as will be appreciated from the method below, the amount of gPAM present in the composition may be dependent on the amount of prepolymer utilized in the method.

The gPAM resin typically has a Mw of at least about 5 megadaltons (MDa). In certain embodiments, the gPAM resin has a Mw of at least about 6 MDa, alternatively at least about 6.5, alternatively at least about 7, alternatively at least about 7.5 MDa. The range of Mw is not particularly limited above the bottom values of these ranges noted (i.e., about 5 MDa or above, alternatively about 5.5 MDa or above, etc.). As such, the gPAM resin may have a Mw in the range of from about 5 to about 90 MDa, such as from about 5 to about 70, alternatively from about 5 to about 50, alternatively from about 10 to about 50, alternatively from about 15 to about 50 MDa.

In specific embodiments, the gPAM resin may have a Mw higher than those listed in the aforementioned ranges. Such gPAM resins may be achieved and provide the benefits of the additive composition disclosed herein. The particular Mw can be selected by one of skill in the art in view of the embodiments shown and described herein, e.g. in view of a desired use or particular application of the additive composition being targeted. Mw determination for the gPAM resin can be carried out using Asymmetric flow field-flow fractionation with multi-angle light scattering (AF4-MALS)

The gPAM resin typically has a radius of gyration (Rg) of at least about 150 nm. In some embodiments, the gPAM resin has a Rg of at least about 160 nm, such as at least about 170, alternatively at least about 180, alternatively at least about 190, alternatively at least about 200 nm, alternatively at least about 210 nm. The range of Rg is not particularly limited above the bottom values of these ranges noted (i.e., about 150 nm or above, etc.). As such, the gPAM resin may have a Rg in the range of from about 150 to about 300 nm, such as from about 175 to about 275, alternatively from about 200 to about 250 nm. In specific embodiments, the gPAM resin may have a Rg higher than those listed in the aforementioned ranges.

The particular relationship of the Mw and the Rg of the gPAM resin results in an extremely dense crosslinked structure. The structural density of the gPAM resin may be expressed in terms of a ratio of Rg/Mw (nm/Mda). Specifically, the gPAM resin typically exhibits a structural density of less than about 20 nm/Mda. For example, in specific embodiments the gPAM resin has a structural density of less than about 15 nm/Mda, as less than about 14, alternatively less than about 13, alternatively less than about 12, alternatively less than about 11, alternatively less than about 10 nm/Mda. The range of Rg/Mw is not particularly limited below the upper values of these ranges noted. As such, the gPAM resin may have a structural density of from about 1 to about 20, such as 1 to about 15, alternatively from about 1 to about 14, alternatively from about 1 to about 13, alternatively from about 1 to about 12, alternatively from about 1 to about 11, alternatively from about 1 to about 10, alternatively from about 2 to about 9 nm/Mda.

It is to be understood that the particular Mw or Rg of the gPAM resin may be selected to achieve a desired structural density (Rg/Mw) and the ultimate performance of the additive composition provided herein. As such, a Mw or an Rg slightly above or below the end points listed above may be utilized to prepare the gPAM resin with a structural density inside one of the listed ranges. Typically, however, the gPAM resin comprises both a Mw and a Rg higher than those of conventional resins, as well as a structural density (Rg/Mw) less than such conventional resins, as demonstrated in the examples herein.

The particular properties and features of the gPAM resin, including those introduced above, will be appreciated in view of the method and components utilized in the preparation method set forth herein.

In general, the method of preparing the additive composition comprises preparing the gPAM resin in the aqueous media, or in another aqueous media which is formulated into the final additive composition. As such, the preparation of the gPAM resin described in detail herein may be used in addition to or in place of conventional processes known in the art.

Preparing the gPAM resin comprises glyoxalating a cationic acrylamide (cAM) prepolymer, i.e., reacting glyoxal with a cAM prepolymer.

The cAM prepolymer may be prepared or obtained. In some embodiments, the method comprises preparing the cAM prepolymer. For example, the preparation may comprise reacting an acrylamide (AM) monomer, a cationic monomer, and optionally one or more additional ethylenically unsaturated monomer(s), in the presence of a chain transfer agent. However, there are multiple methods to prepare the cAM prepolymer, which are known in the art and may be adapted from conventional methods of preparing prepolymers suitable for glyoxalation to give a GPAM resin. Examples include free radical polymerization in water, such as via use of a redox initiating system (e.g. sodium metabisulfite and sodium persulfate). Other combinations of redox initiating systems for initiating polymerization of suitable comonomers may also be used, including other persulfate salts such as potassium persulfate or ammonium persulfate or other components such as potassium bromate. Such redox initiating systems may be used in combination with a chain transfer agent, such as a sodium hypophosphite, sodium formate, isopropanol, or mercapto compound-based chain transfer agent.

The cAM prepolymer typically includes ionic repeat units, e.g. cationic repeat units derived from the cationic monomer. The cationic comonomer may be any cationic monomer capable of reacting through radical chain polymerization with the AM monomer and/or other monomers/comonomers to form the cAM prepolymer.

Examples of cationic monomers include tertiary and quaternary diallyl amino derivatives, or tertiary and quaternary amino derivatives of acrylic acid or (meth)acrylic acid or acrylamide or (meth)acrylamide, vinylpyridines and quaternary vinylpyridines, or para-styrene derivatives containing tertiary or quaternary aminoderivatives. Cationic comonomers may be chosen from diallyldimethylammonium chloride (DADMAC), [2-(acrylamido)ethyl]trimethylammonium chloride, [2-(methacrylamido)ethyl]trimethylammonium chloride, [3-(acrylamido)propyl]trimethyl ammonium chloride, [3-(methacrylamido)propyl]trimethyl ammonium chloride, N-methyl-2-vinylpyridinium N-methyl-4-vinylpyridinium, p-vinylphenyltrimethylammonium chloride, p-vinylbenzyltrimethylammonium chloride, [2-(acryloyloxy)ethyl]trimethylammonium chloride, [2-(methacryloyloxy)ethyl]trimethylammonium chloride, [3-(acryloyloxy)propyl]trimethyl ammonium chloride, [3-(methacryloyloxy)propyl]trimethylammonium chloride, and combinations thereof. It is understood that mixtures of cationic comonomers can be used to the same purpose. In some embodiments, the cationic monomer includes diallyldimethylammonium chloride (DADMAC).

The cationic acrylamide prepolymer may contain other monomer units provided by additional ethylenically unsaturated monomer(s) in the polymerization. These monomers are typically selected to not significantly interfere with the glyoxalation process. For example, additional monomer units can be selected from acrylates, alkyl acrylates (e.g. methacrylates, methyl methacrylate, etc.), hydroxy alkyl acrylates, styrenes, vinyl acetates, alkyl acrylamides (e.g. N-alkyl(meth)acrylamides, N,N-dialkyl(meth)acrylamides, etc.) and the like, as well as combinations thereof. Specific examples of such monomer units include methacrylate, octadecyl(meth)acrylate, ethyl acrylate, butyl acrylate, methyl(meth)acrylate, hydroxyethyl(meth)acrylate, 2-ethylhexylacrylate, N-octyl(meth)acrylamide, N-tert-butyl acrylamide, N-vinylpyrrolidone, N,N′-dimethyl acrylamide, styrene, vinyl acetate, 2-hydroxy ethyl acrylate, acrylonitrile, and the like, and combinations thereof.

In certain embodiments, anionic monomers, or monomers later transformed into anionic group-containing units, are included in or as the other monomers/comonomers to form the cAM prepolymer. It is to be appreciated that the term “cAM prepolymer” as used herein is not limited to only cationic polymers, but instead merely denotes the presence of the cationic monomer described herein. Accordingly, it will be understood by those of skill in the art that the cAM prepolymer may itself be amphoteric in nature, e.g. when anionic monomers are used in the polymerization and/or anionic units are present in the structure of the cAM prepolymer. For example, in some such embodiments one or more anionic monomer is selected from vinyl acidic compounds (e.g. acrylic acid, methacrylic acid, maleic acid, allyl sulfonic acid, vinyl sulfonic acid, itaconic acid, fumaric acid, 2-acrylamido-2-methyl-propanesulfonic acid, etc.), vinyl compounds with potentially-anionic groups (e.g. maleic anhydride, itaconic anhydride), vinyl group-containing salts (e.g. alkali metal and/or ammonium salts of the acidic compounds above, sodium styrene sulfonate, etc.), as well as combinations thereof. Such anionic monomers may be described collectively as vinyl carboxylic acids and esters or salts thereof.

The cAM prepolymer can be prepared with a linear or branched structure, and may be crosslinked or substantially non-crosslinked. It will be appreciated that in particular embodiments, the preparation method utilizes the chain transfer agent introduced above. As such, it sill be understood that the cAM prepolymer may also be chain-transferred, or crosslinked & chain-transferred (i.e., structured).

In some embodiments, the cAM prepolymer is crosslinked, and the preparation method comprises using a crosslinking agent. Typical examples of crosslinking agents are polyethylenically unsaturated compounds, such as methylene bis(meth)acrylamide, triallylammonium chloride, tetraallyl ammonium chloride, polyethyleneglycol diacrylate, polyethyleneglycol dimethacrylate, N-vinyl acrylamide, divinylbenzene, tetra(ethyleneglycol) diacrylate, dimethylallylaminoethylacrylate ammonium chloride, diallyloxyacetic acid, diallyloctylamide, trimethyllpropane ethoxylate triacryalte, N-allylacrylamide, N-methylallylacrylamide, pentaerythritol triacrylate, and the like, as well as salts, derivatives, and combinations thereof. Other systems and agents for crosslinking can be used instead of or in addition to the agents above. For example, covalent crosslinking through pendant groups can be achieved, e.g. by the use of ethylenically unsaturated epoxy or silane monomers, the use of polyfunctional crosslinking agents such as silanes, epoxies, polyvalent metal compounds, etc., or by other known crosslinking systems. In certain embodiments, the cAM prepolymer is prepared using at least one of the anionic monomer units set forth above, and further crosslinked via covalently bonding a linking group using the anionic group of the anionic monomer units.

Polymerization is typically carried out in an aqueous solution (e.g. in the aqueous media) at a temperature of at least about 50° C. It is sometimes advantageous to raise the temperature after the addition of all comonomers has been completed so as to reduce the level of residual monomers in the product. The pH during the reaction may be adjusted with acids or bases or with a buffer, and can be dependent on the initiator system and components used in the reaction.

Comonomers maybe added all at once or added over any length of time. If one monomer is less reactive than another, then it is advantageous to add part or all of the slower reacting monomer at the start of the polymerization, followed by a slow continuous or multiple batch wise additions of more reactive monomer. Adjusting feed rates can lead to more uniformity of the compositions of polymer chains. Likewise, initiators may be added at once or added over any length of time. To reduce the amount of residual monomer in the copolymer, is often advantageous to continue adding the initiator system for some time after all monomers have been added, or to introduce batch wise additional amounts of initiator. Controlling polymer compositional and molecular weight uniformity by controlling addition times is well known in the polymer industry.

In some embodiments, the cAM prepolymer is prepared with at least one predetermined physical property, such as cationic monomer content, Mw, and/or reduced solution viscosity (RSV). For example, the cAM prepolymer typically comprises very low charge, typically with less than about 4 mol % of cationic monomer units derived from the cationic monomer. For example, in general embodiments the cAM prepolymer comprises less than about 3.5, alternatively less than about 3, alternatively less than about 2.5 mol % of cationic monomer units. In some embodiments, the cAM prepolymer comprises from about 0.5 to about 3.5, alternatively from about 1 to about 3.5, alternatively from about 1 to about 3, alternatively from about 1.5 to about 3, alternatively from about 1.5 to about 2.5 mol % of cationic monomer units.

The cAM prepolymer typically has a medium/high Mw of from about 80 to about 130 KDa. In some embodiments, the cAM prepolymer has a Mw of from about 90 to about 130 KDa, alternatively from about 90 to about 120 KDa. The Mw of the cAM prepolymer may be determined by standard procedures and processes, e.g. via SEC/RI.

The cAM prepolymer typically has a RSV of from about 0.5 to about 1.8 dL/g, such as from about 0.6 to about 1.6 dL/g. The RSV of the cAM prepolymer may be determined by standard procedures and processes, e.g. using a PolyVisc.

In certain embodiments, the cAM prepolymer comprises from about 0.5 to about 3.5 mol % of cationic monomer units derived from the cationic monomer, a Mw of from about 80 to about 130 KDa, and exhibits a RSV of from about 0.5 to about 1.8 dL. In specific embodiments, the cAM prepolymer comprises from about 1 to about 3 mol % of cationic monomer units derived from the cationic monomer, a Mw of from about 90 to about 120 KDa, and exhibits a RSV of from about 0.6 to about 1.6 dL/g.

The cAM prepolymer may be characterized by other properties in addition to those above, such as by charge density and/or zeta potential. For example, in some embodiments, the cAM prepolymer typically has a zeta potential of from about 10 to about 30 mV, at pH 7. In some embodiments, the cAM prepolymer has a zeta potential of from about 15 to about 30 mV, such as from about 15 to about 30, alternatively from about 20 to about 30, alternatively from about 20 to about 25 mV, at pH 7. The zeta potential of the cAM prepolymer may be determined by standard procedures and processes, e.g. via using a Wyatt Mobius. In these or other embodiments, the cAM prepolymer typically has a charge density of from about 0.2 to about 3 mEq./g, such as from about 1 to about 3, mEq./g, at pH 7.

The method further comprises glyoxalating cAM prepolymer, i.e., reacting the cAM prepolymer with glyoxal. As demonstrated in the Examples herein, the method may be used to selectively glyoxalate the cAM prepolymer by controlling the concentration of the cAM prepolymer in an aqueous media during glyoxalation. In this fashion, it has been found that the gPAM resin having the high Mw, high Rg, and high structural density described above can thus be prepared, decoupled from the Mw of the cAM prepolymer.

As understood in the art, the reaction the cAM prepolymer with glyoxal may be carried out under varied conditions of time, temperature, pH, etc. Typically, the glyoxal is added quickly to the cAM prepolymer to minimize crosslinking. Alternatively, the cAM prepolymer can be added to the glyoxal. It is also generally understood in the art that the molecular weight of the cAM prepolymer, and the ratio of glyoxal to acrylamide groups on the cAM prepolymer, may be adjusted to achieve desired levels of crosslinking and viscosity build during a glyoxalation process

The cAM prepolymer (A) and the glyoxal (B) are typically reacted in a dry weight (w/w) ratio of from about 75:25 to about 95:5 (A):(B), such as from about 80:20 to about 90:10. The residual level of glyoxal of the final gPAM resin is typically below about 10%, alternatively below about 8%, alternatively below about 5%, on a dry weight basis of the gPAM resin.

The concentration of the cAM prepolymer is selectively controlled during glyoxalation to give the high-Mw gPAM resin. For example, in typical embodiments, the cAM prepolymer is present in the aqueous media at an initial concentration of less than about 4, alternatively less than about 3, alternatively less than about 2% (w/w). In certain embodiments, the prepolymer is present in the aqueous media at an initial concentration of from about 0.5 to about 4, alternatively from about 0.5 to about 3, alternatively from about 0.5 to about 2.5, alternatively from about 0.5 to about 2, alternatively from about 1 to about 2%. This concentration is typically defined in terms of solids, i.e., the weight percent concentration of the starting cAM prepolymer at the start of the glyoxalation reaction, that is when all of the glyoxal has been added. In this fashion, the solids content of the cAM prepolymer and the solids content of the gPAM resin may be described in view of each other. Likewise, selective glyoxalation may be understood to include selecting a desired cAM prepolymer concentration based on a desired gPAM resin solids content in the additive composition.

In some embodiments, the glyoxal concentration during glyoxalation is selectively controlled alongside the concentration of the cAM prepolymer. For example, in specific embodiments, the glyoxal concentration is from about 0.1 to about 1% (w/w) in the aqueous media. In some embodiments, the glyoxal concentration is from about 0.1 to about 0.5, alternatively from about 0.2 to about 0.3%.

The gPAM resins may be adjusted to a pH of about 3 after glyoxalation reaction to improve storage stability until they are used, or may be used directly without further adjustment.

The additive composition may be used in papermaking, e.g. to make a paper or board product. Specifically, the additive composition may be used treat pulp or fiber, in the form of a furnish, web, sheet, etc., with the gPAM resin. The additive composition used in paper making may lead to beneficial properties, such as, e.g. improved dry strength, temporary wet-strength, permanent wet-strength, wet-strength decay, etc., compared to the same properties when a conventional gPAM resin (i.e., of relatively-low Mw) is used.

In the papermaking process there are multiple steps, generally including: forming an aqueous suspension of cellulosic fibers; addition of additives (e.g. the additive composition) to the suspension; forming a sheet from the fibers; and drying the sheet to give the paper. Additional steps may also be employed (e.g. for tissue and towel grades, a step of creping or forming a structure of the paper to provide properties such as softness is typically employed). Moreover, the addition of additives (e.g. the additive composition) may be carried out after sheet formation. These steps and variations of the process are known to those skilled in the art. The additive composition, as strength aid, may be added during any one or more appropriate steps in the papermaking process, e.g. after pulping and before drying.

In view of the above, a process of preparing paper or paperboard is also provided herein. The process generally comprises:

-   -   (1) providing an aqueous suspension of cellulosic fibers;     -   (2) treating the cellulosic fibers with the additive         composition;     -   (3) forming the cellulosic fibers into a sheet; and     -   (4) drying the sheet to produce a paper.

In some embodiments, the process utilizes a difficult furnish, i.e., a furnish with a relatively high content of lignan, and possibly other dissolved and/or suspended colloidal anionic materials. For example, the additive composition is particularly suitable for use in high-kappa furnishes, i.e., furnishes of pulp having a kappa number of at least 25, alternatively at least 30. In certain embodiments, the process comprises treating cellulosic fibers of a pulp having a kappa number of at least 30, alternatively at least 32, alternatively at least 35, alternatively at least 40.

The term “kappa” used herein in the context of the process is to be understood according to the conventional meaning of the industry standard kappa number. As such, it will be understood that kappa numbers are employed as a key test method for determining the content/level of lignin remaining in a sample of finished or in-process pulp. In this fashion, kappa number can be used a measure of the completeness of a given pulping process, and may be used to characterize and/or differentiate types of furnishes on the basis of relative lignin content. The type of pulp is not particularly limited with respect to kappa number determination, with generally-accepted standards being suitable for use in determining kappa numbers across a wide range of pulps, including chemical, semi-chemical, unbleached, semi-bleached, and bleached varieties.

Determining the kappa number of a given furnish can be carried out by use of a strong oxidant (e.g. potassium permanganate), which reacts with lignin as well as small levels of certain other organic impurities remaining in pulp at various process stages. The kappa number of a particular sample may be determined manually (e.g. via laboratory reaction and analysis), or via use of an automated instrument suitable for measuring kappa number. It will be understood that a given procedure and/or instrument may need to be validated based on the particulars of a given standard in order to determine agreement of results with the standard itself. Examples of kappa number standards include Test Method TAPPI/ANSI T 236 om-13 (November 2013), provided by the Technical Association of the Pulp & Paper Industry Inc. (TAPPI) and approved by the American National Standards Institute (ANSI). As written, the TAPPI/ANSI T 236 om-13 standard is intended for use in the laboratory testing of pulps. It is recognized, however, that kappa number is widely used as an in-process test in the pulp and paper mill, in some cases with modifications.

Typically, kappa numbers are reported as a value of from 1 to 100. However, values higher than 100 may be determined, although it is understood that above a kappa number of 100 precision of a given test may decrease. Section 16 of the TAPPI/ANSI T 236 om-13 standard sets forth information regarding unintended or unexpected impact that certain deviations from the standard can have on data accuracy, precision, or both.

In certain cases, the kappa number can be used to quantify, or at least approximate, the lignin content of a particular pulp sample. For example, there is a nearly linear relationship between the kappa number and both Klason lignin and chlorine number for pulps below 70% total yield, such that a kappa number determined according to the TAPPI/ANSI T 236 om-13 standard may be used to approximate the percentage of Klason lignin in a sample according to the equation Lignin level (%)=Kappa number×0.13. However, it is to be understood that there is no general and unambiguous relationship between the kappa number value and the exact content of lignin or other organic impurities across pulps. Rather, any such relationship can vary depending on the wood specie(s), pulping process(es), and delignification procedures employed to obtain the specific pulp prepared. Accordingly, when kappa number is to be used to determine a precise numerical value regarding the amount of lignin present in a specific furnish, such as those suitable for use in the present embodiments, a more precise relationship can be established by testing the pulp therein according to processes and procedures widely known in the art.

The aqueous suspension of cellulosic fibers may comprise virgin and/or recycled fiber. In some embodiments, the aqueous suspension comprises at least 30% virgin fiber, such as at least 70%, alternatively at least 90%, alternatively at least 95%, alternatively at least 99% virgin fibers (w/w), based on the total weight of cellulosic fiber in the suspension. In some such embodiments, the aqueous suspension is an unbleached kraft (UBK) virgin furnish.

In some embodiments, the aqueous suspension comprises recycled fiber. The amount of recycled fiber may vary, and may be used to supplement virgin fiber or as the predominant fiber source in the aqueous suspension. Accordingly, the aqueous suspension may comprise virgin fiber in an amount of at least 1, alternatively at least 5, alternatively at least 10, alternatively at least 20, alternatively at least 30, alternatively at least 50 alternatively at least 75% recycled fiber (w/w), based on the total weight of cellulosic fiber in the suspension. In some embodiments, the aqueous suspension consists of recycled fiber (e.g. as a 100% recycled furnish and/or for use in a 100% recycled furnish mill). It will be understood that recycled fiber may originate from mixed paper grades, old corrugated cardboard (OCC), etc.

It will be appreciated that the steps (2) and (3) may be carried out in any order, as described above and demonstrated in the examples herein. Typically, however, the additive composition will be employed in the wet-end of a papermaking process. For example, in some embodiments treating the cellulosic fibers with the additive composition comprises adding the additive composition to a furnish or a treated form thereof (e.g. a thick stock), such as in an approach system of a paper machine. Alternatively, treating the cellulosic fibers with the additive composition may comprise adding the additive composition

The additive composition may be prepared and subsequently combined with a pre-formed aqueous suspension of cellulosic fibers. For example, the gPAM resin may be prepared and introduced to the suspension within a time period suitable for storage, such as within about 10, alternatively of about 8, alternatively of about 5 hours after glyoxalation. Alternatively, the additive composition may be prepared in the aqueous suspension, i.e., where the gPAM resin is prepared in-situ with the aqueous suspension. Such processes are known in the art as “on-site” processes, and are particularly suitable for use in the present embodiments.

As introduced above, the paper making process may further comprise steps of drying, patterning, treating, and creping the paper to form a finished paper product. Finished paper products can include, but are not limited to, paper, tissue, board, and the like. For example, in some embodiments the process comprises treating an unbleached kraft (UBK) virgin furnish with the additive composition. In these or other embodiments, the proves is used to prepare virgin linerboard. Other products, such as fine paper, fluting, boxboard, etc., may likewise be prepared.

EXAMPLES

The following examples, illustrating embodiments of this disclosure, are intended to illustrate and not to limit the invention. Unless otherwise noted, all solvents, substrates, and reagents are purchased or otherwise obtained from various commercial suppliers (e.g. Sigma-Aldrich, VWR, Alfa Aesar) and utilized as received (i.e., without further purification) or as in a form used conventionally in the art.

General Cationic Acrylamide cAM Prepolymer Synthesis

A reaction flask is charged with DI water, diallyldimethylammonium chloride (DADMAC), a pH modifier, and a chain transfer agent. To the reaction flask two external feeds are connected, one containing acrylamide, the other containing sodium metabisulfite (SMBS) and the chain transfer reagent. The reaction mixture is warmed to 35° C., then ammonium persulfate (APS) and sodium bromate are added, followed by starting the feeds. The acrylamide feed is set to be added over 135 minutes, the SMBS feed is set to be added over 195 minutes. During the acrylamide feed, the reaction is gradually heated through an external heating source at ˜0.4° C./min up to 90° C. After the conclusion of the acrylamide feed, a second portion of APS is added and the reaction is held at 90° C. for one hour. The amount of DADMAC is varied as necessary to make a prepolymer with the acquired amount of cationic monomer. The molecular weight of the prepolymer is manipulated by increasing or reducing the amount of chain transfer agent as necessary.

Synthesis of cAM Prepolymer 1 (PP1)

A four neck roundbottomed flask (hereafter denoted the reaction flask) fitted with an overhead stirrer, nitrogen sparger and temperature probe, was charged with DI water (112 g) and 65% DADMAC (4.510 g, 0.017 mol), adipic acid (0.277 g, 0.0019 mol), and a 1.08% solution of sodium hypophosphite (SHP) (4.43 g, 0.000462 mol), followed by sparging with nitrogen. A single neck roundbottomed flask is charged with 50% acrylamide (120.60 g, 0.847 mol) to which a 40% solution of Trilon-C is added (0.484 g, 0.00038 mol) and is connected to a peristaltic pump (ACM Feed). A trigger solution comprising a 3.5% SMBS solution (4.81 g, 0.00088 mol) and 1.5% SHP solution (4.43 g, 0.000462 mol) is loaded in a 10 mL syringe and put in a syringe pump (Feed 1). The reaction flask is charged with a 15% solution of sodium bromate (0.5820 g, 0.00057 mol) and a 15% solution of ammonium persulfate (0.3583 g, 0.000235 mol), immediately after which the ACM feed (set to 0.89 mL/min) and Feed 1 (set to 3.86 mL/hr) are started. The polymerization is allowed to react adiabatically for 1 hour, then heated at 0.7° C./min for 75 minutes. After the completion of the ACM feed (135 minutes), the nitrogen sparger is removed from the reaction solution and a 15% solution of APS (2.22 g 0.00146 mol) is added initiating the burn out. The temperature is held at 90° C. for one hour, during which time Feed 1 completes. The reaction is then cooled to below 50° C. and transferred to a sample jar.

Synthesis of cAM Prepolymer 2 (PP2)

A four neck roundbottomed flask (hereafter denoted the reaction flask) fitted with an overhead stirrer, nitrogen sparger and temperature probe, was charged with DI water (87 g) and 65% DADMAC (10.02 g, 0.04 mol), adipic acid (0.277 g, 0.0019 mol), and a 1.5% solution of sodium hypophosphite (SHP) (5.13 g, 0.000726 mol), followed by sparging with nitrogen. A single neck roundbottomed flask is charged with 50% acrylamide (138.34 g, 0.938 mol) to which a 40% solution of Trilon-C is added (0.484 g, 0.00038 mol) and is connected to a peristaltic pump (ACM Feed). A trigger solution comprising a 3.5% SMBS solution (5.44 g, 0.0010 mol) and 1.5% SHP solution (5.13 g, 0.000726 mol) is loaded in a 10 mL syringe and put in a syringe pump (Feed 1). The reaction flask is charged with a 15% solution of sodium bromate (0.6590 g, 0.000655 mol) and a 15% solution of ammonium persulfate (0.4057 g, 0.00027 mol), immediately after which the ACM feed (set to 1.02 mL/min) and Feed 1 (set to 4.37 mL/hr) are started. The polymerization is allowed to react adiabatically for 1 hour, then heated at 0.7° C./min for 75 minutes. After the completion of the ACM feed (135 minutes), the nitrogen sparger is removed from the reaction solution and a 15% solution of APS (2.52 g 0.0017 mol) is added initiating the burn out. The temperature is held at 90° C. for one hour, during which time Feed 1 completes. The reaction is then cooled to below 50° C. and transferred to a sample jar.

General Glyoxalation Procedure

A prepolymer (PP) is charged to a reaction flask and diluted with DI water so the concentration of the polymer is as desired, to which is added glyoxal at 15:85 dry w:w ratio relative to the prepolymer. A turbidity of the solution is taken indicating the starting turbidity. The pH is increased to 10.2 using dilute NaOH and this pH is maintained and the turbidity measured every 2 minutes. Once the turbidity increases by a required amount the reaction is quenched by reducing the pH to 4 with dilute sulfuric acid.

Synthesis of GPAM 1

PP1 is used to prepare GPAM 1 according to the general glyoxalation procedure above. A PP1 concentration of 1.6% and a glyoxal concentration of 0.28% are utilized, with the reaction being quenched after a turbidity increase of 15 NTU from the initial reading.

Synthesis of GPAM 2

PP2 is used to prepare GPAM 2 according to the general glyoxalation procedure above. A PP2 concentration of 1.7% and a glyoxal concentration of 0.3% are utilized, with the reaction being quenched after a turbidity increase of 10 NTU from the initial reading.

Determination of Polymer Properties

The prepolymer RSV is determined at 0.25 dL/g in 1 M ammonium chloride using a PolyVisc. Determination of gPAM Mw is done using an AF4-MALS. Parameters and properties of PP1, PP2, GPAM 1, and GPAM 2 are set forth in Table 1 below.

TABLE 1 PP gPAM gPAM Rg/Mw Turbidity DADMAC RSV Mw Rg (nm/ Change (mol %) (dL/g) (MDa) (nm) Mda) (deltaNTU) GPAM 2 0.93 33 216  6.545 15 1 GPAM 4.1 0.95 2.04 120.2 58.922 12 2

As shown, GPAM 1 is a gPAM resin according to the present embodiments, and GPAM 2 is a comparative gPAM resin.

In further examples, shown below, a commercially-available gPAM resin is used and designated “GPAM 3”.

Handsheet Preparation Methods (HS Runs 1-5)

Unbleached virgin kraft pulp was sourced from commercial mills and refined in a cycle beater as received until the CSF was between 550-650 mL. Handsheets were produced using a noble and wood handsheet mold. The quantity of pulp necessary to form ten 90 lb/1000 sqft sheets is added to the proportioner and diluted to 8 L using conditioned water (pH 5; 2000 us/cm). The GPAM is added at 8 lb/ton, followed by a commercial cPAM retention aid at 0.25 lb/ton, and lastly 50% alum at 7.5 lb/ton, with ˜30 seconds between each addition. A sheet is made by dewatering the required amount of treated pulp using a forming wire and deckle box, then pressing the sheet (60 PSI), and finally drying the sheet on a drum dryer (˜118° C.). A total of eight sheets are made for each condition. Each condition was repeated in at least duplicate, resulting in 16 total sheets per condition. For HS Run 3, prior to adding the chemical additives, Indulin-C was added to the proportioner along with a commercial defoamer (0.25 lb/ton). Sheets were then aged in a controlled atmosphere room (50% relative humidity; 23° C.) for at least 48 hours prior to testing. Parameters of HS Runs 1-5 are set forth in Tables 2-3 further below.

Pilot Paper Machine

A furnish made up of unbleached kraft fibers sourced from a commercial mill was dispersed in water adjusted to a pH of 4.5 and this dispersed fiber is treated with additives at any or all of the points described as the thick stock pump inlet and outlets, wet end approach system in order from mixer 1 to 4, thin stock fan pump inlet, outlet, and dilution. The GPAM was applied at mixer 3 at an equivalent dosage of 8 lb/ton, a commercial sizing agent and alum were added at the fan pump outlet at an equivalent dosage of 3 lb/ton, and 4.5 lb/ton respectively. The stock was applied to the paper machine through a flow spreader (hydraulic) head box onto a fourdrinier equipped with three vacuum assisted baffles to remove water forming a wet sheet. The wet sheet was then passed through two single felt presses to mechanically remove water and densify the sheet. The final water removal (drying) is carried out using eleven electrically heated dryer cans before being wound up onto a core at the reel, targeting a basis weight of 125 lb/1000 sqft. Parameters of the Pilot Paper Machine run are set forth in Tables 2-3 further below.

Mechanical Strength Performance of the Paper

Ring crush was measured with a Testing Machines Inc. Model 17-76-00-0001 using TAPPI method T 822 om-16. STFI was measured with a Buchel BV Short Span Compression Tester Model 17-34-00-0001 using TAPPI method T 826 om-21. Mullen Burst was measured with B. F. Perkins Model C Mullen Tester according to standard TAPPI method T 807 om-16. Wet mullen burst was measured in a similar manner to T 807 om-16 but after soaking the paper for 2 hours. For the pilot paper machine, the machine direction performance of the STFI and cross directional performance of ring crush were tested and reported. All strength performance data were normalized to basis weight and are reported relative to the performance of a blank sample, which was treated with all additives except for the gPAM. Parameters and performance of HS Runs 1-5 and the Pilot Paper Machine run according to the measurements described above are set forth in Tables 2-3 below.

TABLE 2 Added Soluble Freeness Lignin Example Kappa (mL) (ppm) HS Run 1 32 602 — HS Run 2 32 602 — HS Run 3 32 602 600 HS Run 4 80 552 — HS Run 5 102 632 — Pilot Paper Machine 80 552 —

TABLE 3 Mullen Burst (Dry)- Mullen Burst (Wet)- Ring Crush-Improvement over Improvement over Improvement over Blank Blank Blank Example GPAM 1 GPAM 2 GPAM 3 GPAM 1 GPAM 3 GPAM 1 GPAM 3 HS Run 1 122% 118% 108% — — — — HS Run 2 116% — 113% — — — — HS Run 3 107% 104% 102% — — — — HS Run 4 108% — 103% — — — — HS Run 5 112% 110% 107% — — — — Pilot Paper 124% — 116% 131% 126% 169% 158% Machine

As shown in Tables 2 and 3 above, when employed in a furnish with a kappa number of 32 (HS Runs 1-3), GPAM 1 exhibits increased performance in the Ring Crush test, even in the presence of soluble lignin, relative to comparative gPAM compositions (i.e., GPAM 2 and GPAM 3). This performance increase holds even in higher kappa furnishes, as shown in HS Runs 4-5.

When employed in a pilot paper machine trial, GPAM 1 exhibits improved but comparable dry strength performance over the comparative gPAM compositions (i.e., GPAM 3). However, GPAM 1 exhibits marked wet strength performance improvements over the comparative gPAM compositions. Such improvements in wet strength under similar conditions have only been demonstrated previously using a combination of wet strength agents, such as conventional gPAM and PAE. The present embodiments achieve superior results, without the detrimental effects of PAE dosing, such as reduced repulpability.

While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims. Moreover, all combinations of the aforementioned components, compositions, method steps, formulation steps, etc. are hereby expressly contemplated for use herein in various non-limiting embodiments even if such combinations are not expressly described in the same or similar paragraphs.

With respect to any Markush groups relied upon herein for describing particular features or aspects of various embodiments, different, special, and/or unexpected results may be obtained from each member of the respective Markush group independent from all other Markush members. Each member of a Markush group may be relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims.

Further, any ranges and subranges relied upon in describing various embodiments of the present invention independently and collectively fall within the scope of the appended claims, and are understood to describe and contemplate all ranges including whole and/or fractional values therein, even if such values are not expressly written herein. One of skill in the art readily recognizes that the ranges and subranges enumerated herein sufficiently describe and enable various embodiments of the present invention, and such ranges and subranges may be further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range “of from 0.1 to 0.9” may be further delineated into a lower third, i.e., from 0.1 to 0.3, a middle third, i.e., from 0.4 to 0.6, and an upper third, i.e., from 0.7 to 0.9, which individually and collectively are within the scope of the appended claims, and may be relied upon individually and/or collectively and provide adequate support for specific embodiments within the scope of the appended claims. In addition, with respect to the language which defines or modifies a range, such as “at least,” “greater than,” “less than,” “no more than,” and the like, it is to be understood that such language includes subranges and/or an upper or lower limit. As another example, a range of “at least 10” inherently includes a subrange of from at least 10 to 35, a subrange of from at least 10 to 25, a subrange of from 25 to 35, and so on, and each subrange may be relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims. An individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims. For example, a range “of from 1 to 9” includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1, which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims. Lastly, it will be understood that the term “about” with regard to any of the particular numbers and ranges described herein is used to designate values within standard error, equivalent function, efficacy, final loading, etc., as understood by those of skill in the art with relevant conventional techniques and processes for formulation and/or utilizing compounds and compositions such as those described herein. As such, the term “about” may designate a value within 10, alternatively within 5, alternatively within 1, alternatively within 0.5, alternatively within 0.1, % of the enumerated value or range.

While the present disclosure has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications will be obvious to those skilled in the art. The appended claims and this disclosure generally should be construed to cover all such obvious forms and modifications, which are within the true scope of the present disclosure. 

1. An additive composition for papermaking, comprising: an aqueous media; and a glyoxalated polyacrylamide (gPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150 nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda.
 2. The additive composition of claim 1, wherein the glyoxalated polyacrylamide resin comprises the reaction product of (A) a cationic acrylamide (cAM) prepolymer and (B) glyoxal in an aqueous media, and wherein: (i) the cAM prepolymer (A) is present in the aqueous media at an initial concentration of from about 0.5 to about 4 wt. %; (ii) the cAM prepolymer (A) and the glyoxal (B) are reacted in a dry weight (w/w) ratio of from about 75:25 to about 95:5 (A):(B); or (iii) both (i) and (ii).
 3. The additive composition of claim 2, wherein the glyoxalated polyacrylamide (gPAM) resin has a weight average molecular weight (Mw) of at least about 6 MDa, wherein the cAM prepolymer (A) is present in the aqueous media at an initial concentration of from about 1 to about 2.5 wt. %, and wherein the cAM prepolymer (A) and the glyoxal (B) are reacted in a dry weight (w/w) ratio of from about 80:20 to about 90:10 (A):(B).
 4. The additive composition of claim 2, wherein the cAM prepolymer (A) comprises the reaction product of: (A1) an acrylamide (AM) monomer; (A2) a cationic monomer; and optionally, (A3) one or more additional ethylenically unsaturated monomer(s); wherein the cAM prepolymer (A) comprises from about 0.5 to about 3.5 mol %, alternatively from about 1 to about 3 mol % of cationic monomer units derived from the cationic monomer (A2).
 5. The additive composition of claim 4, wherein the cAM prepolymer (A):(i) comprises from about 1 to about 3 mol % of cationic monomer units derived from the cationic monomer (A2); (ii) has a reduced solution viscosity (RSV) of from about 0.6 to about 1.6 dL/g; or (iii) both (i) and (ii).
 6. The additive composition of claim 4, wherein the AM monomer (A1), the cationic monomer (A2), and optionally the additional ethylenically unsaturated monomer(s) (A3) are reacted in the presence of a chain transfer agent.
 7. The additive composition of claim 4, wherein: (i) the AM monomer (A1) comprises acrylamide; (ii) the cationic monomer (A2) comprises diallyldimethylammonium chloride (DADMAC); (iii) the one or more additional ethylenically unsaturated monomer(s) (A3), when present, are selected from styrenes, alkyl acrylates, vinyl acetates, and vinyl carboxylic acids, esters, or salts thereof; or (iv) any combination of (i)-(iii).
 8. The additive composition of claim 2, wherein the cAM prepolymer (A) has a reduced solution viscosity (RSV) of from about 0.5 to about 1.8 dL/g.
 9. A method of preparing an additive composition for papermaking, comprising: I) preparing a cationic acrylamide (cAM) prepolymer having a cationic monomer content of less than about 3.5 mol %; and II) selectively glyoxalating the cAM prepolymer by controlling the concentration of the cAM prepolymer in an aqueous media during glyoxalation to give a glyoxalated polyacrylamide (gPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150 nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda.
 10. The method of claim 9, wherein the weight average molecular weight (Mw) of the glyoxalated polyacrylamide (gPAM) resin is at least about 6 MDa.
 11. The method of claim 9, wherein the cAM prepolymer (A) comprises: (i) a cationic monomer content of from about 1 to about 3 mol %; (ii) a reduced solution viscosity (RSV) of from about 0.5 to about 1.8 dL/g; or (iii) both (i) and (ii).
 12. The method of claim 9, wherein (II) selectively glyoxalating the cAM prepolymer comprises reacting the cAM prepolymer (A) and glyoxal (B) in an aqueous media, and wherein: (i) the cAM prepolymer (A) is present in the aqueous media at an initial concentration of from about 0.5 to about 2.5%; (ii) the cAM prepolymer (A) and the glyoxal (B) are reacted in a dry weight (w/w) ratio of from about 80:20 to about 90:10 (A):(B); or (iii) both (i) and (ii).
 13. The method of claim 9, further comprising preparing the cAM prepolymer (A), wherein preparing the cAM prepolymer (A) comprises reacting (A1) an acrylamide (AM) monomer, (A2) a cationic monomer, and optionally (A3) one or more additional ethylenically unsaturated monomer(s) in the presence of a chain transfer agent, and wherein the cAM prepolymer (A) comprises from about 0.5 to about 3.5 mol % of cationic monomer units derived from the cationic monomer (A2).
 14. The method of claim 13, wherein the cAM prepolymer (A) comprises from about 1 to about 3 mol % of cationic monomer units derived from the cationic monomer (A2).
 15. The method of claim 13, wherein: (i) the AM monomer (A1) comprises acrylamide; (ii) the cationic monomer (A2) comprises diallyldimethylammonium chloride (DADMAC); (iii) the one or more additional ethylenically unsaturated monomer(s) (A3), when present, are selected from styrenes, alkyl acrylates, vinyl acetates, and vinyl carboxylic acids, esters, or salts thereof; or (iv) any combination of (i)-(iii).
 16. The method of claim 15, wherein the one or more additional ethylenically unsaturated monomer(s) (A3) are present in the reaction of the AM monomer (A1), the cationic monomer (A2), and the chain transfer agent, and wherein the one or more additional ethylenically unsaturated monomer(s) (A3) is selected from styrenes, alkyl acrylates, vinyl acetates, and combinations thereof.
 17. A process of forming paper, said process comprising: (1) providing an aqueous suspension of cellulosic fibers; (2) combining the additive composition of claim 1 with the aqueous suspension; (3) forming the cellulosic fibers into a sheet; and (4) drying the sheet to produce a paper.
 18. The process of claim 17, wherein the aqueous suspension of cellulosic fibers: (i) comprises a kappa number of at least about 30; (ii) comprises unbleached kraft (UBK) virgin fiber; (iii) comprises recycled fibers; (iv) is substantially free from polyamidoepichlorohydrins (PAE); or (V) any combination of (i)-(iv).
 19. The process of claim 18, wherein the aqueous suspension of cellulosic fibers comprises a mixture of virgin fibers and recycled fibers.
 20. The process of claim 17, wherein the gPAM resin is prepared in-situ within about 5 hours of combining the additive composition with the aqueous suspension. 